Decomposition characteristics of returned rapeseed straw in soil and effects on soil fertility

The burning of straw in open air, straw stacking or abandoning are not only resource-wasting, but also seriously impact surrounding environments, traffic safety, social production and people lives. Although the promotion of rapeseed straw decomposition and rural crop straw utilization limits the negative impacts of straw burning on the environment and improves soil fertility, so far not much research has been conducted on rapeseed straw decomposition rate of rice-rapeseed rotation system in Jiang-Huai area. Different amounts of rapeseed straw were returned to soil at various buried depths in nylon net bags in the experiment. The decomposition characteristics of the returned rapeseed straws and the effect on soil fertility and crop yield were determined. The results showed that the decomposition ratio of rapeseed straw after being returned to the field increased with time. The decomposition rate of rapeseed straw was faster at the initial stage of decomposition but then slowed down right through the final stage of decomposition. Straw decomposition rate was negatively correlated with the amount of returned rapeseed straw to the field. The order of decomposition rate was entire amount straw returned to soil < 2/3 amount straw returned to soil < 1/2 amount straw returned to soil < 1/3 amount straw returned to soil. The decomposition rate of returned rapeseed straw on surface soil was faster than that in the 20 cm soil depth. Also the decomposition rate of returned rapeseed straw in the 10 cm soil depth was the lowest. Returning straw to soil improved soil physical and chemical properties. Not only did it reduce soil bulk density, but it also enhanced soil organic matter and nutrients in comparison with control treatment (KC) at P < 0.05. Returning rapeseed straw to soils increased rice yield. Yield of CK treatment was 7 725 kg·hm^-2. Also compared with CK, yields of different returned straw-to-soil treatments increased in the range of 6.02%~21.17% (P< 0.01). The study therefore provided the basis for controlling rapeseed straw decomposition rates to promote straw resource utilization and improve agricultural eco-environment.